Field of the Invention
The invention is based on a device for detecting a leak in a fuel supply system in an internal combustion engine, and, more particularly, to a device for detecting a leak in a fuel supply system in an internal combustion engine during an engine overrunning and for detecting which of several injection values is leaking.
In motor vehicles with an internal combustion engine, the fuel is pumped out of the fuel tank with the aid of an electric fuel pump and fed to the injection valves via fuel lines. Excess fuel typically returns to the tank via a return line. In order that an adequate quantity of fuel will always be available, the fuel is pumped by the electric fuel pump at an overpressure, and the electric fuel pump is regulated in a suitable way, for instance by measuring the fuel pressure and using it for evaluation.
In some fuel supply systems, the return line is dispensed with, and the fuel supply quantity regulation is demand-based. In both fuel supply systems it is mandatory that a leak or defect in the fuel circulation be detected with certainty and reliably, because otherwise, on the one hand, escaping fuel or incident fuel vapors could lead to emissions that exceed legal limits; on the other, defective injection valves might cause engine damage, if fuel were unintentionally able to reach an engine cylinder through the leaking injection valves.
In response to this problem, methods and apparatus have already been disclosed with whose aid leaking injection valves can be detected, or with whose aid leak detection is carried out in conjunction with a tank venting system. Such methods and apparatus are described for instance in German published, unexamined patent applications DE-OS 42 43 178 or DE-OS 40 40 896. In DE-OS 42 43 178, a method is disclosed in which leaking injection valves are detected by also firing cylinders into which fuel has not yet been injected, each time the engine is started. If such ignitions cause the rpm to increase perceptibly, then the association valve must be leaking, allowing fuel to enter the affected cylinder.
In the method and apparatus for checking the intactness of a tank venting system as disclosed in DE-OS 40 40 896, a test is done to find whether the negative pressure building up in the tank varies in a predictable way after the tank venting valve is opened. To that end, the entire system is monitored for functionality, and the system is assessed as nonfunctional if the negative-pressure buildup gradient is below a predeterminable threshold value.
Both known systems for detecting leaks in a portion of the fuel supply system of an internal combustion system are either rather complicated, or fail to guarantee that leak detection is possible throughout the entire fuel supply system.